Parahexyl

Parahexyl, also known as synhexyl, is a synthetic homologue of tetrahydrocannabinol (THC) which was invented in 1941 during attempts to elucidate the structure of Δ⁹-THC, one of the active components of cannabis.^[2][3][4]

Parahexyl

Clinical data
Other names	Synhexyl, n-hexyl-Δ3-THC, (C6)-Δ6a(10a)-THC
Drug class	Cannabinoid
ATC code	none
Legal status
Legal status	BR: Class F2 (Prohibited psychotropics)[1] CA: Schedule II DE: Anlage I (Authorized scientific use only) UK: Class B US: Schedule I UN: Psychotropic Schedule I
Identifiers
IUPAC name 3-n-hexyl- 7,8,9,10-tetrahydro- 6,6,9-trimethyl- 6H-dibenzo(b,d)pyran- 1-ol
CAS Number	117-51-1 Y
PubChem CID	8334
ChemSpider	8031 Y
UNII	450N174F9W
KEGG	C22779
CompTox Dashboard (EPA)	DTXSID90861748
Chemical and physical data
Formula	C22H32O2
Molar mass	328.496 g·mol−1
3D model (JSmol)	Interactive image
SMILES Oc2cc(cc1OC(C\3=C(/c12)CC(CC/3)C)(C)C)CCCCCC
InChI InChI=1S/C22H32O2/c1-5-6-7-8-9-16-13-19(23)21-17-12-15(2)10-11-18(17)22(3,4)24-20(21)14-16/h13-15,23H,5-12H2,1-4H3 Y Key:OORFXDSWECAQLI-UHFFFAOYSA-N Y
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Parahexyl is similar in both structure and activity to THC, differing only in the position of one double bond and the lengthening of the 3-pentyl chain by one CH₂ group to n-hexyl.^[5] Parahexyl produces effects typical of other cannabinoid receptor agonists in animals. It has a somewhat higher oral bioavailability than THC itself but is otherwise very similar.^[6] Presumably, it acts as a CB₁ receptor agonist in the same way as THC, but as there has been no research published using parahexyl since the discovery of the CB₁ receptor, this has not been definitively confirmed.

Parahexyl was occasionally used as an anxiolytic in the mid-20th century, the dosage ranging from 5 mg to 90 mg.^[7][8]

Parahexyl was made illegal under UN convention in 1971 on the basis of its structural similarity and similar effects profile to THC. Parahexyl was placed into the most restrictive Schedule I^[9] as a compound with no medical use.

Isomerism

At least three isomers of parahexyl have been studied and are known to be active as cannabinoids. Parahexyl itself (i.e. the Δ^6a(10a) isomer) has not had any significant use in scientific research since it was banned internationally in the early 1980s; however, the Δ⁸ and Δ⁹ isomers are both known to be cannabinoid receptor agonists, and Δ⁸-parahexyl has the code number JWH-124,^[10][11] while Δ⁹-parahexyl has been isolated from Cannabis plant material and assigned the name tetrahydrocannabihexol (THCH).^[12]

Dibenzopyran and monoterpenoid numbering of tetrahydrocannabinol derivatives

7 double bond isomers of parahexyl and their 30 stereoisomers
Dibenzopyran numbering			Monoterpenoid numbering		Number of stereoisomers	Natural occurrence	Convention on Psychotropic Substances Schedule
Short name	Chiral centers	Full name	Short name	Chiral centers
Δ6a(7)-parahexyl	9 and 10a	3-hexyl-8,9,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ4-parahexyl	1 and 3	4	No	unscheduled
Δ7-parahexyl	6a, 9 and 10a	3-hexyl-6a,9,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ5-parahexyl	1, 3 and 4	8	No	unscheduled
Δ8-parahexyl	6a and 10a	3-hexyl-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ6-parahexyl	3 and 4	4	No	unscheduled
Δ9,11-parahexyl	6a and 10a	3-hexyl-6a,7,8,9,10,10a-hexahydro-6,6-dimethyl-9-methylene-6H-dibenzo[b,d]pyran-1-ol	Δ1(7)-parahexyl	3 and 4	4	No	unscheduled
Δ9-parahexyl	6a and 10a	3-hexyl-6a,7,8,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ1-parahexyl	3 and 4	4	No	unscheduled
Δ10-parahexyl	6a and 9	3-hexyl-6a,7,8,9-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ2-parahexyl	1 and 4	4	No	unscheduled
Δ6a(10a)-parahexyl	9	3-hexyl-7,8,9,10-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol	Δ3-parahexyl	1	2	No	Schedule I

Note that 6H-dibenzo[b,d]pyran-1-ol is the same as 6H-benzo[c]chromen-1-ol.

See also: Tetrahydrocannabinol § Isomerism

See also

• Delta-3-Tetrahydrocannabinol (delta-3-THC)
• Hexahydrocannabihexol (HHCH)
• Tetrahydrocannabutol
• Tetrahydrocannabiphorol (THCP)
• Tetrahydrocannabivarin (THCV)